2 times i have put food in the oven while it was preheating to 350 with convection oven button. have owned oven for almost 3 years. twice the oven just keeps preheating so hot that i get an error f10 and we have to go and shut off main breaker to shut off stove. it locks us out and you can't turn it off or reset. is this a problem i should call a repairman for or am i doing something wrong. i am afraid of fire. please advise what is an F10 error? Kenmore model #790.97423901 Serial #VF93448620